1. Field of the Invention
Embodiments of the invention generally relate to a system and a method for supporting a web in a polishing system.
2. Background of Invention
In semiconductor wafer processing, the use of chemical mechanical planarization, or CMP, has gained favor due to the enhanced ability to increase device density on a semiconductor workpiece, or substrate, such as a wafer. As the demand for planarization of layers formed on wafers in semiconductor fabrication increases, the requirement for greater system (i.e., process tool) throughput with less wafer damage and enhanced wafer planarization has also increased.
CMP systems generally include a polishing head, a platen and polishing material disposed on the platen. A substrate retained in the polishing head is pressed against the polishing material and moved relative to the polishing material in the presence of a polishing fluid. Abrasives, typically contained in the polishing fluid or polishing material, remove material from the surface of the substrate synergistically with the chemical activity provided by the polishing fluid.
One type of polishing material that includes abrasives disposed therein is known as abrasive sheet material. The abrasive sheet material comprises a plurality of abrasive particles suspended in a resin binder that is disposed in discrete elements on a backing sheet. As the abrasive particles are contained in the polishing material itself, systems utilizing abrasive sheet material generally use polishing fluid that do not contain abrasives. Such polishing fluids enhance the service life of their fluid delivery systems.
Abrasive sheet polishing material is generally available in stick-down form but is often utilized in the form of a web. Generally, the web is periodically advanced over the course of polishing a number of substrates as the polishing surface of the web is consumed by the polishing process. A vacuum is typically applied between the web and platen to fix the web to the platen during the polishing process wherein the platen and web are related. When the web is advanced, the vacuum is removed, freeing the web from the platen's surface.
However, indexing the web across a polishing platen is sometimes difficult. Polishing debris and other contaminants may clog the vacuum system and prevent the removal of the vacuum between the web and platen. Additionally, fluids that come in contact with the web may cause surface tension or attraction to develop between the web and the underlying surface of the platen. This surface tension must be over-come to accomplish advancement of the web. If the attraction between the web and platen is great, the indexing means may not be able to index the web or the web may become damaged during the indexing process.
Providing a cushion of gas between the web and platen assists in overcoming the attraction between the web and platen. The gas lifts the web to a spaced-apart relation to the platen where the web may be freely indexed. However, providing gas to the area between the web and platen is complicated, and requires rotary union and process tubing to be routed through an already crowded platen.
Therefore, there is a need for an improved platen assembly for handling a web of polishing material in a polishing system.